An aliphatic polyamide typified by nylon 6 or nylon 66 has excellent properties such as heat resistance, chemical resistance, rigidity, abrasion resistance, and moldability, and hence is used for a variety of applications as an engineering plastic. In electrical and electronic fields, the aliphatic polyamide is required to have high flame retardance based on a UL94 standard, and hence many methods of imparting flame retardance using a variety of flame retardants have been proposed and put to practical use. However, such aliphatic polyamide has high water absorbability, and hence there causes a problem in that a molded article produced from the polyamide changes in dimension and reduces in its physical properties. Further, in recent years, in the electrical and electronic fields which require imparting of flame retardance, a method called surface mount technology (SMT) has been rapidly spread for the purposes of high-density mounting of parts, promotion of the efficiency of a soldering step, and the like. Therefore, the conventional resin has become ineffective in terms of heat resistance as well.
Meanwhile, recently, a semi-aromatic polyamide which contains, as a major component, a polyamide formed of 1,6-hexanediamine and terephthalic acid and is called 6T polyamide has also been used in the electrical and electronic fields which require flame retardance. For example, Patent Documents 1 and 2 each propose a technology for imparting flame retardance to a semi-aromatic polyamide such as the 6T polyamide.
However, the polyamide formed of 1,6-hexanediamine and terephthalic acid has a melting point of about 370° C., and hence cannot be used actually because melt polymerization and melt molding need to be carried out at a temperature equal to or higher than a polymer degradation temperature. Therefore, in actual use, adipic acid, isophthalic acid, ε-caprolactam, or the like is copolymerized at about 30 to 40 mol % to prepare a polyamide having a composition to achieve a melting point as low as about 320° C. which falls within a temperature range that enables actual use of the polyamide. Such copolymerization of a third component or a fourth component is effective for lowering the melting point, but may lead to lowering of a crystallization rate and a final crystallization degree. As a result, not only physical properties such as rigidity, chemical resistance, and dimensional stability at high temperature are lowered, but also productivity may be lowered due to elongation of a molding cycle. Further, changes in physical properties such as dimensional stability caused by water absorption are modestly improved through the introduction of an aromatic group compared to the conventional polyamide, but the problem has not been solved actually.